Aqueous metal coordination compounds as protective coatings for glass

ABSTRACT

Coordination compounds having good stability in aqueous systems are used to treat glass surfaces at elevated temperatures, the coordination compounds being represented by the general formula Y 2  MX 6  wherein Y is an alkali metal, hydrogen or ammonium, M is tin, titanium or zirconium and X is a halogen, generally fluorine or chlorine. The glass surfaces so treated are rendered chemical resistant and when treated by conventional cold-end coatings exhibit excellent strength, scratch resistance and chemical durability.

This is a division of application Ser. No. 8,291, filed 01/31/79 nowU.S. Pat. No. 4,232,065.

The subject invention relates to the treatment of glass surfaces forsuch articles of commerce as jars, bottles, tumblers and the like andparticularly to the treatment of the outer surfaces of such articleswhich may be subjected to an abrasive contact with similar articles orwith equipment associated with the manufacture or handling of sucharticles.

When glass articles are first formed they have their maximum strengthsubsequent to their formation, but such articles lose their strength asa result of abrasion and scratching as they contact each other duringsubsequent operations including filling, capping and packaging.According to the particular products with which they are filled, suchglass articles may also be subject to washing, sterilizing or vacuumtreatment resulting in additional abrasive contact against other glassarticles and equipment.

As is known in the art, the problem of contact abrasion to glassware hasbeen substantially alleviated by various protective surface treatmentsthat are applied immediately upon formation or at least prior topackaging of the glass articles. One basic surface treatment relates tovapor deposition wherein prior to annealing various metallic compoundsthat pyrolitically decompose upon contact with heat are applied tofreshly formed glass to render metallic oxide surface layers on theglass articles. Exemplary of a widely used metallic oxide treatment isthe formation of tin oxide on glass surfaces by exposure to stannicchloride vapors. The tin oxide surface treatment, when present in filmsless than that which would cause objectionable light interference andiridescence, produces a surface condition which, when further coatedwith an organic lubricating material, is lubricous and highly resistantto abrasion damage. A somewhat similar mechanism may be employedutilizing titanium tetrachloride.

While stannic or titanium halides do not decompose to form a metallicoxide layer on glass surfaces until exposed to temperatures in the orderof about 600° F., to 1200° F., it has been found that titanium orstannic chloride vapors are subject to hydrolysis through exposure tomoisture associated with the immediate atmosphere. Because of themoisture it has been necessary to protect the treatment gases fromhydrolysis by utilizing moisture-free inert gases or properlyconstructed equipment. At any rate, the problem of maintaining arelatively water-free condition has in and of itself created substantialprocessing difficulties. In spite of the various systems to preventhydrolysis of these metallic compounds it still does occur in actualpractice to some degree and has posed problems in that stillobjectionable by-products are formed, viz, highly acidic products areformed that corrode and pollute the working environment.

The present invention relates to a particular family of specialprotective coating compositions that are applied not by vapor depositionprocesses but by spray processes utilizing a water base without thenoxious and objectionable vapors of the prior art that often corrode theenvironment. The subject water-base compositions when applied providesstrengthening, lubricity, scratch resistance, water resistance, lusterand other properties such as stability at high temperatures.

Accordingly, an object of the instant invention is to provide protectivecoatings for glass articles.

Another object of the present invention is to provide an improvedprotective coating for simple application at the hot end of a glassforming machine as a water surface spray for glass articles.

Another main object of the present invention is an improved protectivecomposition comprising stable coordinating compounds containing tin,titanium or zirconium along with fluorine or chlorine.

Further, another object of the present invention is to provide ahaze-free protective coating for increasing the strength as well asscratch resistance and chemical durability of glass articles.

Another object of the present invention is to provide an aqueous spraysystem for hot-end coating newly formed glass articles having no noxiousor objectionable characteristics as associated with previous anhydrousSnCl₄ and TiCl₄ materials.

Other and further objects of the invention will be obvious upon anunderstanding of the illustrative embodiments about to be described orwill be indicated in the appended claims, and various advantages notreferred to herein which would occur to one skilled in the art uponemployment of the invention in practice.

Strength and chemical durability improvements in glass articles arehighly desirable since they permit the use of thinner-walled articleswhich reduces the cost thereof. In the past glassware is often treatedinternally in order to curtail detrimental decomposition of the insidewalls of ware. This treatment is generally necessary for certaincontainers, especially those that house liquors and pharmaceuticalgoods. In the past, glassware has been treated with sulfur oxidecompounds to improve the chemical durability or inertness of the ware.However, the sulfur oxides were not entirely successful due to thetoxicity and operational hazards encountered. More recently, glasswarehas also been treated with various decomposablechloro-fluorohydrocarbons while the ware is above the decompositiontemperature of these compounds. These prior art approaches have theirlimitations. The coordination compounds herein disclosed provideeffective chemical durability when applied to the external and internalportions of hot glassware.

One aspect of the subject invention relates to decreasing the tendencyof glass surfaces to exhibit atom or ion interchange with contactingphases associated with boundary phenomenon. In accordance with thisinvention there is described a method and articles formed by treatingthe surfaces of glassware while at an elevated temperature with asolution containing a coordination compound, said compound beingrepresented by the formula Y₂ MX₆ wherein Y is an alkali metal, hydrogenor ammonium, M is titanium, tin or zirconium and X is a halogen.Furthermore, in accordance with the present invention there is alsoprovided a method of increasing the abrasion resistance and strength ofa glass article, said method comprising applying to the surface of saidglass article while at an elevated temperature an aqueous solutioncontaining coordination compound having the general formula Y₂ MX₆wherein Y is an alkali metal, hydrogen or ammonium, M is titanium, tinor zirconium and X is a halogen, the temperature of the glass beingsufficient to immediately and substantially completely vaporize thewater content of said solution, the temperature of the glass being atleast about 425° C., and above the decomposition temperature of saidcoordination compound, annealing said article so treated at atemperature of at least about 590° C., to thereby decompose saidcoordination compound on the surface of said glass article, andthereafter treating said article with water insoluble organic compoundselected from the group consisting of polyethylene, polypropylene,polystyrene, polyurethane, fatty acids and their derivatives andmixtures thereof.

The particular family of compounds that have been found mostadvantageous in carrying out the subject invention are those compoundswhich may be referred to as coordination compounds having a central atomof a metal such as titanium, zirconium or tin and having an oxidationnumber of +4 and coordination number of 6 with the oxidation numbers ofthe liquid being from zero for YX and 1 for X. The class of coordinationcompounds embraced herein include the types which may be represented bythe general formula MX₄ (YX)₂ wherein M=Ti, Sn, or Zr, X=F, Cl, Br, Iand Y=NH₄, Na, K, H, Li or other quaternary amines. Those compounds maybe readily prepared by known inorganic methods of synthesis and formwater stable compositions. These coordination compounds may be readilydissolved in water and may be admixed in a range from between about 2and about 50 weight percent in accordance with this invention. Thesesolutions may be readily applied to hot glass articles and are highlyreactive therewith at the hot end of an individual section glass formingmachine. The solutions may be readily applied by simple sprayingtechniques whereby a thin film of the solutions is deposited upon thehot glass surface.

There are a large number of organic compounds that may be used to coatthe glass surface after exposure to the coordination compounds hereindescribed. Thus, the glass article that has been previously treated inwith the coordination compound is progressively cooled over a period oftime and then subject to a treatment such as by spraying of an organicmaterial. These organic materials are generally olefinic polymers. Anexample of such organic materials may be cited polyethylene,polypropylene, polystyrene, polyurethane, polyvinyl alcohols, fattyacids and their derivatives and mixtures thereof.

The term "hot-end" coating means a treatment applied to hot glassobjects very shortly after forming while the objects are still hot fromforming, i.e., from the forming temperature down to approximately 600°F., for soda-lime glass objects, the normal temperature range beingapproximately 1100° F., to about 800° F. Hot-end treatment in accordancewith this invention improves glass object surface properties such asabrasion resistance when coupled with an organic "cold-end coating."Hot-end treatments also reduce hot-end damage such as belt checks,hot-end scuffs and glass sticking which function to reduce the strengthof glass object.

The term "cold end" coating means a treatment after annealing to provideglass objects with improved lubricity and/or abrasion resistance,usually in combination with an inorganic "hot end" treatment as alreadystated. Cold end chemicals are usually organic chemical based and areapplied generally at between about 200°-400° F.

After the glass articles are coated with the coordination compoundsherein described, they enter an annealing lehr, are heated, and arethereafter progressively cooled to about 400° F., and lower when theyare exposed to an organic material, generally an aqueous compositioncontaining olefin polymers or alkali metal salts of fatty acids, asalready described. When the second coating is dried, the resultantcoated article in accordance with this invention has a scratchresistance value which is unexpectedly and superior to that of a glasssurface having either coating alone and are at least equivalent to onecoated by conventional titanium and tin chloride as employed in theprior art.

As regards the application of the aqueous solution of the coordinationcompounds, the temperature of the glass is not too critical, provided itis sufficient to promote formation of the desired coating. Inparticular, the temperature of the glass articles should be greater thanabout 590° F., and preferably greater than 700° F., to ensure forming ofa clear, haze-free coating. Glass temperatures in the range of fromabout 900° F., to about 1100° F., are preferred. As for the secondcoating, the temperature of the articles should be about 200° F., toabout 400° F.

The process and composition of this invention find particular utility inproviding a hot-end coating for glass containers. For such use, it isreadily employed by spraying the glass container after emergence fromthe forming machine and before entering the annealing lehr.

Although there are several theories under which the particular class ofcoordination compounds react with the hot glass surface it ishypothesized that increased chemical durability arises from the fluorineligands attached to the central metal atom and the HF produced when NH₄F is thermally decomposed. It is further theorized that the sodium,potassium, calcium and other metallic ions including magnesium andaluminum react with the fluorine to form unreactive fluoride salts inglass. Such fluoride compounds are known to be extremely inert and waterinsoluble because of the high crystal lattic energy of the fluoride,compounds so formed. At any rate, the resulting surface treated by thecompositions herein described function, inter alia, to improve articleabrasion resistance particularly when coupled with an organic lubricantto reduce the tendency for hot-end damage and provide a decorativeeffect at high coating levels as well as improve the glass surface'sresistance to corrosive attack by aqueous systems.

The invention may be appropriately illustrated by the followingExamples:

EXAMPLE I

An aqueous solution was prepared containing about 14 weight percent(NH₄)₂ TiF₆ (0.75 molar) with 0.1 weight percent octylaphenoxypolyethoxy ethanol (Triton X-100) and was sprayed using an AmericanGlass Research Pentahood employing four spray guns rendering a totalflow of 1.28 ml/sec on newly formed 8 oz., soda-lime glass jars. Theconveyor rate was approximately 60 ft., per minute and the glass surfacetemperature was about 1000° F. Following this hot-end treatment thecontainers were passed into an annealing lehr and thereafter annealed atabout 1100° F., and then the containers were cold-end coated at about300° F., with polyethylene based material by using a standard overheadspray means.

EXAMPLE II

An aqueous solution was prepared containing about 36 weight percent(NH₄)₂ SnCl₆ (about 0.75 molar) and applied by spraying directly on hotcontainers using the equipment of Example I except the conveyor speedwas 120 ft./min. and a total solution flow of about 3.0 ml/sec for thefour spray guns. After annealing at about 1100° F., an organic fattyacid was used as cold-end treatment.

EXAMPLE III

An aqueous solution was prepared containing about 12 weight percent H₂TiF₆ (about 0.75 molar) and directly applied to 8 oz., soda-lime glassbaby food containers that were previously heated in a muffle furnace forabout one hour at about 1150° F., and thereafter sprayed for about 6seconds using a Campbell Hausfeld gun employing about 50 psi airpressure from two feet and at a solution flow rate of about 1.4 ml/sec.The treated containers where thereafter reheated for thirty minutes atabout 1150° F., to similate annealing. After completion of this laststep the glass containers were given an organic fatty acid cold-endtreatment by heating the samples for thirty minutes at 280° F.

EXAMPLE IV

An aqueous solution of about 7.6 weight percent H₂ TiF₆ (about 0.45molar) was prepared as in Example I. This solution was applied to babyfood jars as recited in Example III. An identical solution was preparedexcept that it included a concentration of 5 weight percent NH₄ F (about1.5 molar) annealed and thereafter treated with a fatty acid cold-endtreatment.

The above containers from Examples I-IV were subjected to the HartfordReflectance Meter and scratch testing equipment to determine the degreeof abrasion resistance. In this procedure two treated containers weremoved across each other at a constant rate with from about 5 to about 75pounds loading, scratching or abrasion was noted by an audiblescratching sound. The average of the lowest loads determined at firstscratch was then recorded. The higher the average the greater theabrasion resistance and the containers from Examle I were evaluated bythis procedure without scratching noted through the entire loadingscheme. An average of about 75 pounds was then reported as the maximumwhereas those with only cold-end treatment averaged about 9 to about 15pounds at first scratch. It was noted that freshly formed glasswarewithout hot-end treatment and cold-end treatment scratched readily atabout 5pounds minimum load. The Hartford Reflectance Meter was employedto determine the average hot-end coating level which in all cases wasapproximately 22 to 35 angstroms computed at TiO₂. All the glasscontainers were clear with no indication of objectionable white haze.The samples of Example II gave a reading of about 70 to about 76 poundsload at first scratch and gave a coating level of about 32±4 angstromscomputed as SnO₂. As for Example III the average scratch resistance wasabout 30±4 pounds load at first scratch, whereas without hot-endtreatment the average was about 9±2, and the average hot-end coatinglevel as about 15±3 angstroms. As regards Example IV the average warescratch resistance was about 3 to 9 pounds without NH₄ F additive and 68to 78 pounds with the NH₄ additive. The average ware hot-end coatinglevels were approximately 8 angstroms and 28±6 angstroms (TiO₂)respectively.

EXAMPLE V

This Example relates to the chemical durability of internal glasssurfaces of glassware. Eight-ounce baby food jars were treated with 0.75m concentration of the coordination compounds as indicated in thefollowing table:

    ______________________________________                                        Internal Treatment    Titrant Volume                                          ______________________________________                                        A.     H.sub.2 O            1.30 ± 0.71 ml                                 B.     (NH.sub.4).sub.2 TiF.sub.6                                                                       0.35 ± 0.07                                      C.     (NH.sub.4).sub.2 ZrF.sub.6                                                                       0.75 ± 0.64                                      D.     (NH.sub.4).sub.2 TiCl.sub.6                                                                      0.50 ± 0.00                                      E.     1,1-difluoroethane.sup.a                                                                         0.16 ± 0.09                                      F.     Control (water blank)                                                                            0.00 ± 0.00                                      ______________________________________                                         .sup.a One cfh with air at 20 cfh for one second each.                   

Except for the 1,1-difluoroethane, all treatments were via Badger airbrush, spraying 0.4 ml inside the preheated container for about 5seconds from a distance of 15 cm with rotation of the container ofapproximately 100 rpm. The internal treatment for Samples B, C and D hadabout 0.1 percent octylphenoxy polyethoxy ethanol therein along with theabove-cited amount of coordination compound. One hundred and fiftymillileters of distilled water was placed in the treated containers andretorted for about one hour at 15 psi pressure. The resulting solutionswere then titrated with 0.02 N H₂ SO₄ to phenolphthalein end point. Thehigher the quantity of acid required is indicative of higher sodiummigration and less chemical durability to sodium leaching during retort.

The compositions herein include the coordination compounds and suchcompositions are easily handled and applied by regular air sprayequipment or atomization mounted adjacent to conventional handlingconveyors. The protective coatings therefore may be applied with littleor no major changes in the normal glassware procedure of moving theglassware from the forming apparatus through the regular annealing lehrand other conventional glassware treating processes and apparatus.

It will be seen that an improved aqueous protective coating system hasbeen disclosed herein for glassware, particularly suited for sprayapplication which exhibits significantly improved protective propertywhen combined with conventional secondary coatings, such as polyethylenecoatings. Improved characteristics such as scratch resistance andchemical durability are markedly improved by the coating combined withgood clear color and lustre characteristics.

The foregoing detailed description has been given for clearness ofunderstanding only, and no unnecessary limitations are to be understoodtherefrom. The invention is not limited to the exact details shown anddescribed, for obvious modifications will occur to those skilled in theart.

What is claimed is:
 1. A coated glass article having improved chemicaldurability and scratch resistance, said coated article being formed byapplying to the surface of said article while it is at a temperature ofat least 425° C., an aqueous solution comprising of from 5 to about 30weight percent of compound having MX₆ ⁻² ions wherein M is titanium, tinor zirconium and X is a halogen, said M being the central atom in thecompound and having an oxidation number of +4 and a coordination numberof 6, the temperature of the glass being sufficient to immediately andsubstantially completely vaporize the water content of said solution,annealing said coated article, applying thereafter to said article anorganic material selected from the group consisting of polyethylene,polypropylene, polystyrene, polyurethane, and fatty acids and theirderivatives and mixtures thereof.
 2. A coated glass article havingimproved chemical durability, said coated article being formed byapplying to the surface a coordination compound at a temperature of atleast 425° C., and above the decomposition temperature of saidcoordination compound, said compound being represented by the formula Y₂MX₆ wherein Y is an alkali metal, hydrogen or ammonium, M is titanium,tin or zirconium and X is a halogen, said M being the central atom inthe compound and having an oxidation number of +4 and a coordinationnumber of 6, said article having a titrant value less than about 0.75 mlof 0.02 N H₂ SO₄, the coating formed by said compound being greater thanabout 8 angstroms and having a ware scratch resistance of more than 30pounds load abrasion to audible scratching.
 3. The coated article ofclaim 2 wherein the halogen is fluorine.
 4. The coated article of claim2 wherein the halogen is chlorine.